This invention relates to water swellable absorbent articles made from crosslinked polyelectrolytes, methods for their preparation, and to an aqueous solution consisting of polyelectrolytes containing free carboxylic groups which is useful to make absorbent articles.
It is known from U.S. Pat. Nos. 3,669,103 (Harper, et al.) and 3,670,731 (Harmon) that cross-linked polymeric sorbents can be sandwiched between flexible supports to achieve disposable diapers or dressings.
It is further known from U.S. Pat. Nos. 2,988,539 (Cohen et al.); 3,393,168 (Johnson); 3,514,419 (Darlow et al.) and 3,557,067 (Burns et al.) that water swellable cross-linked carboxylic copolymers can be prepared. However, these prior art copolymers are all crosslinked during copolymerization or crosslinked after polymerization with subsequent neutralization of the carboxylic acid groups to form water swellable polyelectrolytes and hence these prior art polyelectrolytes cannot be crosslinked in situ as a coating on a substrate or as a flexible film thereof.
It is further known from Ser. No. 468,794, filed May 9, 1974 that carboxylic synthetic polyelectrolytes can be crosslinked after polymerizaton by the use of a nucleophilic displacement reaction using polyhaloalkanols, sulfonium zwitterions, haloepoxy alkanes, polyglycidyl ethers and mixtures thereof. The advantage of the present invention over this technique is that the crosslinking reaction proceeds by an acid catalyzed elimination reaction of the N-substituted amide crosslinker with the carboxylic polyelectrolytes to achieve crosslinked and swellable polyelectrolytes.